, and substitute with a rover V8 block...... which i think actually was originally a chevvy V8 block.
Very close. It's a Buick lump. All the same GM family though, GM bought Buick in 1908.
Story was, someone from Rover visited Buick's engine design department in Detroit. He discovered the alloy V8 there, asked about it, and was told that GM had decided not to manufacture it. Rover first put it in their P5B (B = Buick), as an alternative to the 3 litre straight six. The rest is history.
History lesson over.